advances in wlans - chungbuk.ac.krcommlab.chungbuk.ac.kr/lab/lecture2/lecture2_1/12....

MobiLight 2010, 12 May 2010, Barcelona

Tutorial on radio communications:

From the basics to future developments

Part 3: Advances in wireless LANs

Oliver Hoffmann

Dortmund University of Technology, Germany

[email protected]

2MobiLight 2010, 12 May 2010, Barcelona

Outline

• Motivation: What is a WLAN?

• Advances of WLANs

• Conclusion and future prospects

3

What is a WLAN?

Typical definitions are ambiguous, lots of exceptions:


WLAN WPAN

Coverage rangeoutdoor: few 100 meters

indoor: few rooms/house

outdoor: ~10 m

indoor: one room

Data rates very high ultra-high

Transmit power moderate low

Power consumption moderate, not critical low, critical

Costs moderate low

Usage portable mobile

Topologyinfrastructure mode

with access to wired network

ad-hoc connection

between devices

Network size can be large small

Connection duration long short

4

What is a WLAN?

Possible definition I: Very high data rates over medium/long ranges


PHY data rate

Coverage

PAN

LAN

WAN

1 Mb/s 10 Mb/s 100 Mb/s 1 Gb/s 10 Gb/s

LTE-A

MAN

IEEE 802.11ac

60 GHz

IEEE 802.16m

WiMedia

THzGiga-IRIEEE

802.15.7BAN

100 kb/s10 kb/s

Bluetooth

v2

IEEE

802.15.4

(ZigBee)

IEEE 802.15.6

5

What is a WLAN?

Possible definition I: Very high data rates over medium/long ranges

Possible definition II: IEEE 802.11 = WLAN, IEEE 802.15 = WPAN


PHY data rate

Coverage

PAN

LAN

WAN

1 Mb/s 10 Mb/s 100 Mb/s 1 Gb/s 10 Gb/s

LTE-A

MAN

IEEE 802.11ac

60 GHz

IEEE 802.16m

WiMedia

THzGiga-IRIEEE

802.15.7BAN

100 kb/s10 kb/s

Bluetooth

v2

IEEE

802.15.4

(ZigBee)

IEEE 802.15.6

IEEE 802.11

has no

competitor in

the WLAN

area

6

WLAN applications

Originally designed for data communication and networking, the

applications of WLANs are becoming more and more diverse


Environments

Home

Enterprise

Small office

Outdoor

Campus, hospital

Car and large vehicles

Factory

7

WLAN applications




Category IEEE 802.11ac/ad usage model

Wireless Display

Desktop display & storage at home or enterprise;

Projection from PC to TV; In room gaming; Streaming from

a camcorder to a display; Broadcast TV field pick-up

8

WLAN applications





Wireless Display




Distribution of HDTV and

other media content

Video streaming throughout the home or large vehicles;

Networking in the office; Remote medical assistance

Rapid upload/download

Rapid sync-n-go file transfer; Picture-by-picture viewing;

Airplane docking; Video content download to car; Police /

surveillance car upload

9

WLAN applications





Wireless Display




Distribution of HDTV and

other media content

Video streaming throughout the home or large vehicles;

Networking in the office; Remote medical assistance

Rapid upload/download

Rapid sync-n-go file transfer; Picture-by-picture viewing;

Airplane docking; Video content download to car; Police /

surveillance car upload

Backhaul Multi-media mesh backhaul; Point-to-point backhaul

Outdoor campusVideo demos or telepresence in auditoriums/lecture halls;

Public safety mesh

Manufacturing floor Manufacturing floor automation

Source: Cisco

10

QoS requirements


With the extended field of WLAN applications, the QoS

requirements are becoming more diverse and more challenging

quasi error-free transmission, low latency, support of a large data rate range

IEEE 802.11 needs continuous advancement

Application Offered load (Mb/s) Max. PLR Max. delay (ms)

Internet streaming AV 0.1 – 4 10-4 200

HDTV 19.2 – 24 10-7 200

Blu-ray 50 10-7 20

Interactive Gaming >100 10-2 10

Lightly compressed video (H.264) 200 10-7 20

Uncompressed video

(1080p, 24 bit/px, 60 frames/s)3000 10-8 10


Outline



– Overview

– High throughput WLAN @ 2.4 and 5 GHz (IEEE 802.11n)

– Vehicular WLAN @ 5.9 GHz (IEEE 802.11p)

– Very high throughput WLAN @ 5 GHz (IEEE 802.11ac)

– Very high throughput WLAN @ 60 GHz (IEEE 802.11ad)

– Further amendments


12

IEEE 802.11

standard and amendments


IEEE 802.11-2007 Base standard including all amendments until 2007

IEEE 802.11a-1999 OFDM PHY @ 5 GHz

IEEE 802.11b-2001 DSSS PHY enhancement: 5.5 and 11 Mbit/s

IEEE 802.11c-1998 Wireless bridging (now part of IEEE 802.1D-2004)

IEEE 802.11d-2001 Global harmonization

IEEE 802.11e-2005 MAC enhancements for QoS

IEEE 802.11F-2003 Interworking of APs in the distribution system (withdrawn)

IEEE 802.11g-2003 Extended rate PHY @ 2.4 GHz (OFDM, DSSS/CCK, PBCC, DSSS-OFDM)

IEEE 802.11h-2003 Spectrum and transmit power management @ 5 GHz in Europe

IEEE 802.11i-2004 MAC security enhancements

IEEE 802.11j-2004 Half rate OFDM PHY @ 4.9 GHz–5 GHz (Japan)

IEEE 802.11k-2008 Radio resource measurement

IEEE 802.11n-2009 Enhancements for higher throughput

IEEE 802.11r-2008 Fast roaming

IEEE 802.11w-2009 Protected management frames

IEEE 802.11y-2009 3.65 – 3.7 GHz operation in the USA

13

IEEE 802.11

task groups


Task group TopicPlanned

release

IEEE 802.11mb 802.11 accumulated maintenance changes Jun. 2011

IEEE 802.11p Wireless access for the vehicular environment (WAVE) Jun. 2010

IEEE 802.11s Mesh networking Jan. 2011

IEEE 802.11u Interworking with external networks Sep. 2010

IEEE 802.11v Wireless network management Sep. 2010

IEEE 802.11z Extensions to direct link setup Sep. 2010

IEEE 802.11aa Robust streaming of audio video transport streams Oct. 2011

IEEE 802.11ac Very high throughput <6 GHz Dec. 2012

IEEE 802.11ad Very high throughput at 60 GHz Dec. 2012

IEEE 802.11ae QoS management, prioritization of management frames Jun. 2012

IEEE 802.11af WLAN in the TV white space Jun. 2011


Outline



– Overview







15

Overview on IEEE 802.11n


Transmission technique OFDM

Frequency bands 2.4 and 5 GHz

Channel bandwidth

(data subcarrier)

M: 20 MHz (52)

O: 40 MHz (108)

OFDM symbol durationM: 4 µs

O: 3.6 µs (short GI)

Modulation M: BPSK up to 64-QAM

FECM: BCC

O: LDPC

Code rates M: 1/2, 2/3, 3/4, 5/6

MIMO: Spatial StreamsM: 1, 2 (APs), direct mapping

O: 3, 4, TxBF, STBC

PHY Data ratesM: 6.5 – 65 (APs: 130) Mb/s

O: 6 – 600 Mb/s

Spectral efficiency 0.3 – 15 bit/s/Hz

PHY MAC

Man. planeControl plane

Protection

Frame

aggregation

RIFS burst

Enhanced

Block Ack

TxBF control

Fast link

adaptation

Reverse

direction

grant

Phased coexistence operation

Power save multi-poll

20/40 MHz

BSS

Channel

switching

Data plane

Mandatory Optional

16

IEEE 802.11n

transmitter block diagram


InterleaverConstellation

Mapper

Scra

mb

ler

En

co

der

pars

er

FE

C e

nco

der

FE

C e

nco

der

Str

eam

pars

er


mapper


Mapper


Mapper

ST

BC

CSD

CSD

CSD

Sp

ati

al m

ap

pin

g

IDFTInsert GI

and window

Analog

and RF

IDFTInsert GI

and window

Analog

and RF

IDFTInsert GI

and window

Analog

and RF

IDFTInsert GI

and window

Analog

and RF

17

IEEE 802.11n MIMO techniques


Spatial division

multiplexing

(direct mapping)

Spatial expansionSpace-time

block coding

Receiver diversity Transmit beamforming

18

IEEE 802.11n MIMO techniques


2.4 GHz band, 20 MHz, 64-QAM, R=5/6MMSE equalizer, considers PHY impairments, synchronization, channel estimation, phase tracking

6.7 dB

STBC vs. RX diversity (MRC): 3.2 dB offset => 3 dB transmit

power penalty, 0.2 dB impairment susceptibility

9.8 dB

TxBF with singular vector decomposition, channel state

information determined from noisy channel estimate

Channel model B (residential), NLOS,

two spatial streams (MCS 15)

Channel model D (typical office), NLOS,

SDM with two spatial streams (MCS 15),

all others with one spatial stream (MCS 7)

19

IEEE 802.11n frame aggregation


A-MSDU A-MPDU

Max. length (Byte) 3839 or 7935 8191 or 16383 or 32767 or 65535

Max. number of subframes no limitation 64

Receiver the same for all subframes

Traffic identifier(s) the same for all subframes can be different

Subframe recovery not possible possible

Implementation HW, buffering of MSDUs possible SW, delay of channel access possible, more complex

A-MSDU A-MPDU

MSDULength Padding

FCS Tail+Pad

Destination

Address

Source

Address

Bytes: 6 6 2 0-2304 0-3

MAC

Header

A-MSDU subframe 1

PHY

HeaderA-MSDU

A-MSDU subframe 2 … A-MSDU subframe n

MPDU

max. A-MSDU length: 3839 or 7935 Byte

MPDUCRC Padding

Tail+Pad

ReservedMPDU

Length

Bytes: max. 4095 0-3

PHY

Header

A-MPDU subframe 1

A-MPDU

A-MPDU subframe 2 … A-MPDU subframe n

PSDU

max. A-MPDU length: 65535 Byte

Delimiter

Signature

4 (MPDU Delimiter)

MSDU or

A-MSDU

20

MAC throughput with

IEEE 802.11n frame aggregation


One video transmission in the 2.4 GHz band, PER = 10%, max. 7 retransmissions,

64-QAM, R=5/6, short GI, EQM, SDM

without frame aggregation with frame aggregation

O. Hoffmann, „Efficient Configurations for Wireless Home Area Networks Based on IEEE 802.11n,“ ITG Symposium on Electronic Media "Systems,

Technologies, Applications", TU Dortmund, March 2009

O. Hoffmann, R. Kays, „Efficiency of Frame Aggregation in Wireless Multimedia Networks based on IEEE 802.11n,“ accepted for publication at the 14th

IEEE International Symposium on Consumer Electronics (ISCE2010), Braunschweig, June 2010

21

Coverage range of IEEE 802.11n


2x2, SDM, 40 MHz, 2.4 GHz, channel model B (residential),

1000 Byte MSDU size, 17 dBm transmit power, noise figure 10 dBThroughput vs. Range, 2X2X40, Channel B

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 90 100

Range (m)

Th

rou

gh

pu

t (M

bp

s)

BPSK,R=1/2

QPSK,R=1/2

QPSK,R=3/4

16-QAM,R=1/2

16-QAM,R=3/4

64-QAM,R=2/3

64-QAM,R=3/4

64-QAM,R=5/6

BPSK,R=1/2,2X

QPSK,R=1/2,2X

QPSK,R=3/4,2X

16-QAM,R=1/2,2X

16-QAM,R=3/4,2X

64-QAM,R=2/3,2X

64-QAM,R=3/4,2X

64-QAM,R=5/6,2X

FLA

IEEE 802.11-04/0895r6


Outline



– Overview







23

IEEE 802.11p: Wireless access

for the vehicular environment

• Origin: Dedicated short range communication (DSRC) to be used by intelligent

transportation systems (ITS)

• Diverse applications: Car-to-car, car-to-infrastructure; e.g. toll collection, safety

• Regulation bodies allocated exclusive frequency band for DSRC– Europe: 5.855 – 5.925 GHz, 5/10/20 MHz spacing, 33 dBm max. EIRP

• IEEE 802.11p defines PHY and MAC– PHY based on IEEE 802.11a, 10 MHz channel bandwidth, max. 27 Mb/s PHY rate, higher receiver

performance requirements, stricter transmission masks, targeted coverage range up to 1 km

– MAC: possibility to immediately communicate without establishing a BSS, modified channel

access parameters (AIFSN values, TXOP limits)

– Status: TG since Sep. 2004, current version D11.0 (March 2010), 2nd SA sponsor ballot

recirculation closed on 8 April 2010, planned release in January 2011

• Higher layer protocols defined by IEEE 1609– IEEE 1609.1: Architecture

– IEEE 1609.11: Secure electronic payments


IEEE 802.11p PHY

IEEE 802.11p MAC

IEEE 1609.4 Multi-channel operation

LLC

IP

TCPUDPIEEE 1609.3

Networking services

IEE

E 1

609.2

Secu

rity


Outline



– Overview







25

IEEE 802.11ac

Very high throughput @ 5 GHz

Goals

• Max. multi-station throughput > 1 Gb/s

• Max. single link throughput > 500 Mb/s

• Higher range of operation

• Reduce power consumption (peak and average)

• Increase spectrum efficiency

• Improve user experience

Approach

• Design by committee

• Ad-hoc groups: PHY, MAC, MU-MIMO, Coexistence

• Status: Composing first draft until Nov. 2010

• Planned Release: Dec. 2012


26

IEEE 802.11ac enhancements

under discussion

Multiple access techniques

• Multi-user (MU)-MIMO as extended SDMA concept

– Simultaneously transmit different spatial streams to different users

– Complex implementation, requires precoding and user scheduling

• Linear precoding (unitary, zero-forcing)

• Non-linear precoding (dirty paper coding)

– CSI required at transmitter

– Users interfere

– MU diversity can be exploited


27


under discussion


• Multi-user (MU)-MIMO as extended SDMA concept

– Simultaneously transmit different spatial streams to different users

– Complex implementation, requires precoding and user scheduling

• Linear precoding (unitary, zero-forcing)

• Non-linear precoding (dirty paper coding)

– CSI required at transmitter

– Users interfere

– MU diversity can be exploited

Achieves 11ac throughput goals

without 80 MHz mode, moderate

MAC efficiency, and more antennas

only at powerful devices (e.g. APs)

Only DL MU-MIMO is considered


IEEE 802.11-09/0303r1

28


under discussion



• OFDMA

– Exclusively assign specific users a subset of data subcarriers

– Comparable complexity of OFDMA on downlink as MU-MIMO on downlink

– Better performance with CSI, but not required

– No interference between users

– MU diversity can be exploited when CSI is available

Does not increase max. throughput, only improves efficiency with multiple lower

rate and mixed clients

frequencypilot subcarriers

data subcarriers of user #1, user #2, user #3, user #4, user #5

29


under discussion

• Increase channel bandwidth to 80 MHz

– Doubles PHY rate at negligible cost increase

– Complex coexistence methods necessary in case of adjacent channels or significant

receiver complexity in case of non-adjacent channels

– Number of available bonded non-overlapping 80 MHz channels very limited (4 in EU)

– New proposals for 160 MHz option (March 2010)

• Higher order modulation (256-QAM, EQM in single-user case)

– Simple enhancement of the architecture

– Lower robustness, higher TX and RX requirements

Benefit for short range, direct link applications

• More antennas, more spatial streams

– SU: NSS ≤ 8; MU: NSTS ≤ 4 per user, NSTS ≤ 8 summed over all users

– Linear increase of PHY rate, some benefit in certain environments

– Feasible only for large, powerful devices like APs



Outline



– Overview







31

60 GHz basics

Regulation in Europe

• 8 GHz unlicensed spectrum

• Max. EIRP: 40 dBm

• Max. transmit power: 10 dBm

Typical channelization

• Four channels of 2.16 GHz each

• 12 narrow channels of 98 MHz each

(IEEE 802.15.3c & WirelessHD)

• Channel bonding (Ecma International)


32

60 GHz characteristics


Challenges

• High pathloss

– Higher free space attenuation

– Higher attenuation by oxygen

absorption, objects, and persons

Directional communication

Appropriate beamforming concepts

Device discovery

CSMA/CA is problematic

• Higher Doppler shift

• Higher phase noise

• Very high sampling rate required

Sophisticated circuit design

IEEE 802.15-10/0149r1

ETSI TR 102 555 V1.1.1

33

60 GHz characteristics


• Ultra-broad, unlicensed frequency band

• Spatial reuse exploitable

– Increase aggregated capacity

– Reduce interference

• Reduced multipath propagation effects

– Single carrier (SC) PHY attractive

alternative

BenefitsChallenges

• High pathloss

– Higher free space attenuation

– Higher attenuation by oxygen

absorption, objects, and persons

Directional communication

Appropriate beamforming concepts

Device discovery

CSMA/CA is problematic

• Higher Doppler shift

• Higher phase noise

• Very high sampling rate required

Sophisticated circuit designO. Hoffmann, R. Kays, R. Reinhold, “Coded Performance of OFDM and SC PHY

of IEEE 802.15.3c for Different FEC Types,” IEEE Global Communications

Conference (GLOBECOM 2009), Honolulu, Hawaii, November 2009

IFFTZF

Equalizer

CP

insertionH

CP

removalFFT

ChannelOFDM

MMSE

Equalizer

CP

insertionH

CP

removalFFT

ChannelSCBT

IFFT

34

60 GHz standardisation


Forum Status TT

Max.

PHY rate

[Gb/s]

FEC MAC Remarks

IEEE

802.15.3c

Released in

Sep. 2009

SC

OFDM

5.28

3.807

RS/LDPC

RS & CC

Central,

802.15.3

Focus on point-to-point,

WirelessHD PHY integrated

ECMA-387Released in

Oct. 2008

SC

OFDM

6.35/25.402

4.234RS & CC

decentral,

WiMedia

Networking of

heterogeneous device types

IEEE

802.11ad

TG, CFP,

Release

> Dec. 2012

OFDM

SC~7 LDPC

Enhances

802.11 MAC

Wide influence of WiGig, use

market penetration and maintain

user experience of 802.11

WiGigReleased v1.0

in Dec. 2009

OFDM

SC7 LDPC

Enhances

802.11 MAC

>10m with beamforming, also for

low power devices, fast session

transfer between 2.4/5/60 GHz

WirelessHDReleased v1.0

in Oct. 2007OFDM 3.807 RS & CC Central

Proprietary, focus on A/V

streaming without HDMI cabling,

DRM concept

35

IEEE 802.11ad

Standardization

• TG since Dec. 2008

• Issued call for proposals (75% approval required)

– Presentation of complete proposals or new techniques at March and May

meetings 2010

– Wide influence of WiGig Alliance (Intel, Broadcom, Marvell, Atheros, NXP,

STM, Samsung, Toshiba, Microsoft, Nokia, TI, Dell, Panasonic, NEC…)

• Will present complete proposal based on WiGig spec. v1.0 at May

meeting 2010, very likely to become initial draft, maybe some slight

modifications

• High number of voters present

– March 2010: 7 new techniques presented, 9 strawpolls, all failed approval

– May 2010: 3 complete proposals, 27 new techniques

• Initial draft planned for Sep. 2010

• Release planned for Dec. 2012


36

IEEE 802.11ad enhancements:

WiGig PHY

• Unified and interoperable PHY

– Common preamble, common MCS, common coding, common packet structure

• SC PHY (mandatory)

– Low power, low complexity transceivers

– Optional low power SC PHY with RS coding

• Control PHY (mandatory)

– based on SC PHY

• LDPC coding

– Four codes of common codeword length of 672 bits, Code rates: 1/2, 5/8, 3/4, 13/16

– Cyclic shifted identity construction


Sample rate 2.64 GHz

FFT size (data, pilot) 512 (336, 16)

Subcarrier spacing 5.15625 MHz

Guard interval 128 samples, 48.4 ns

Symbol duration 242 ns

Modulation QPSK up to 64-QAM

PHY rates 693 – 6756.75 Mb/s

Chip rate 1.76 GHz

Chips per block (data, guard) 512 (448, 64)

Chip time 57 ns

Modulation BPSK up to 16-QAM

PHY rates 385– 4620 Mb/s

• OFDM PHY (optional)

High performance on

frequency selective channels

37


WiGig MAC

• Personal basic service set (PBSS)

– Enhance IBSS mode to accommodate directionality

– Introduce network coordination by PBSS central point

• Channel access supporting directionality and spatial frequency reuse

• Flexible beamforming scheme

– Tunable to simple, low power devices but also to complex devices

– Two phases: sector level sweep and beam refinement protocol

– Supports beam tracking


BT A-BFT AT CBP 1 SP 1 SP 2 CBP 2

time

Beacon interval

Data transmission time

CBP: Contention-based period

(EDCA tuned for directional access)

SP: Service period

BT: Beacon Time

A-BFT: Association beamforming training

AT: Announcement time

38


WiGig MAC

• Enhanced security

– GCMP: Galois/Counter mode (128-bit AES)

• Coexistence mechanisms

– Same channelization as other 60 GHz systems

– Energy detection, interference mitigation, transmit power control, dynamic frequency

selection

• Fast session transfer

– Enable transition of communicating stations to another supported band

(2.4, 5 or 60 GHz)


band B1, channel C1,

MAC addr. M1

band C2, channel B2,

MAC addr. M1


MAC addr. M2


MAC addr. M3

band C2, channel B2,

MAC addr. M3


MAC addr. M4

Transparant FST

Non-transparant FSTSTA 1 STA 2


Outline



– Overview







40

Further amendments

IEEE 802.11s (TG since May 2004)

• Need for extended range, need for mobile infrastructure, need for flexible, fail-safe networks

Mesh networking for configuring and using an IEEE 802.11 wireless distribution system

• Auto-configuring paths (at MAC layer!) between stations over self-configuring multi-hop

topologies using radio-aware metrics; automatic topology learning

• Allow for alternative path selection metrics and/or protocols (reactive/proactive)

• Status: Current version D5.0 (Apr. 2010), WG letter ballot (421 comments), planned release

in Jan. 2011

IEEE 802.11v (TG since Dec. 2004)

• No solution from IEEE 802.11 to manage and configure stations, only insufficient and

complex other solutions (e.g. SNMP)

PHY/MAC extensions to enable wireless network management

• Centralized and distributed operation, coherent upper layer interface

• Create appropriate AP management information base

• Status: Current version D10.0 (Mar. 2010), 2nd SA sponsor ballot recirculation closed on

14 Apr 2010, planned release in Sep. 2010


41

Further amendments

IEEE 802.11u (TG since Aug. 2004)

• No or proprietary interworking with external networks like cellular systems, e.g. for charging

in an IEEE 802.11 hotspot infrastructure

PHY/MAC enhancements to support interworking with external networks

• Enhanced protocol exchanges over the air, primitives for interaction with upper layers

• Status: Current version D9.0 (Apr. 2010), 1st SA sponsor ballot recirculation closed on

23 Apr. 2010, planned release in Sep. 2010

IEEE 802.11z (TG since Aug. 2007)

• Inefficient communication between two stations via the AP => direct link setup (DLS) in 11e

• Upgrade necessary, WMM without DLS => Lack of DLS capable APs

Extensions to DLS to operate with non-DLS capable APs and support power save mode in

active DLS session (only between exactly two stations)

• Tunneled DLS: Specific Ethertype encapsulation to tunnel DLS frames through an AP

• Power saving: Periodic wake-up schedule or unscheduled automatic power save delivery

• Status: Current version D8.0 (Apr. 2010), 2nd SA sponsor ballot recirculation closed on

4 May 2010, planned release in Sep. 2010 (competitor: Wi-Fi Direct with soft-AP)


42

Further amendments

IEEE 802.11aa (TG since Mar. 2008)

• QoE of video streaming with IEEE 802.11 is not always satisfactory

MAC enhancements for robust video streaming

• Graceful degradation (tag packets as drop eligible without deep packet inspection)

• Increased robustness in OBSS without centralized management entity

• Intra-AC prioritization by modifying EDCA parameter set (e.g. two alternative ACs)

• Improved link reliability and low jitter characteristics for multi-/broadcast video streams

• Status: Compose D1.0 for May meeting, planned release in Oct. 2011

IEEE 802.11ae (TG since Dec. 2009)

• A lot of amendments defined crucial management frames, some require instantaneous

reaction

Mechanisms for prioritization of management frames using existing mechanisms of

medium access for improved support of QoS

Examples: Radio resource measurement, wireless network management, channel

feedback frames of 11n/ac/ad, emergency services, location tracking, mesh path selection

• Status: Call for technical presentations, initial draft in Nov. 2010, release in Sep. 2012


43

Further amendments

IEEE 802.11af

PHY and MAC modifications for channel access and coexistence in the TV white space

(TV broadcasting frequencies in the VHF/UHF bands)

• Very attractive frequency bands due to smaller pathloss, but:

– Higher delay spread, smaller coherent bandwidth, primary users

Subcarrier spacing may be higher than coherent bandwidth

Guard interval may not suffice to mitigate ISI

Preamble may not be long enough for channel estimation

• International inhomogeneity:

– Different TV channel bandwidths (6/7/8 MHz)

– Different number and allocation of available TV channels (max. 47 – 910 MHz)

OFDM with fixed subcarrier spacing and different FFT sizes (64/128/256 or more)

Different guard interval durations (up to 12.8 µs)

5/10/20/40/80 MHz operation, find suitable channelization

Coexistence mechanisms like scanning and quiet periods

• Status: TG since Dec. 2009, compose D1.0 for May meeting, release in June 2011



Outline



– Overview







45

Conclusion

• WLANs provide an installation-free, flexible, low cost solution for a vast

amount of applications

• IEEE 802.11 is THE standard family for WLANs

• High market penetration for years to come

• IEEE 802.11 provides a very powerful toolbox

Efficient exploitation is the key, but beyond the scope of the standard

• IEEE standardization process is crucial but takes too long– Standard too late for the market, provokes proprietary solutions

• 75 % approval requirement leads to inclusion of many optional “features”– Causes thousands of comments and years of comment resolution

Limit down selection

50% approval for initial draft

75 % approval for WG and SA ballots


46

Future prospects

• For reasons of efficiency, implementation effort and energy consumption, the use of one single technology for all transmission tasks is not expedient

Map transmission tasks to technology hierarchy, which results from the trade-off between data rate and coverage range/robustness


47

HomeGateway

Sat receiver

LocalServer

WLAN 1

WLAN 2

Control/Sensor Network

WPAN

Future prospects

Some research work

• Determine the optimum toolbox

configurations

• Overcome limited interaction between

vertical and horizontal layers

• Scalable hardware implementation of

network nodes

• Technology improvement, e.g. robust

control network

• Convergence of WLAN and fiber (RoF)

• Green communication


Vision

48

Recommended background

reading

• Eldad Perahia, Robert Stacey, “Next Generation Wireless LANs: Throughput, Robustness, and Reliability in 802.11n,” Cambridge University Press, 28 August 2008

• Benny Bing, “Emerging Technologies in Wireless LANs: Theory, Design, and Deployment,” Cambridge University Press, 5 November 2007

• Yang Xiao, Yi Pan, “Emerging Wireless LANs, Wireless PANs, and Wireless MANs: IEEE 802.11, IEEE 802.15, 802.16 Wireless Standard Family,“ John Wiley & Sons, 29 April 2009

• Bernhard H. Walke, Stefan Mangold, Lars Berlemann, “IEEE 802 Wireless Systems: Protocols, Multi-Hop Mesh/Relaying, Performance and Spectrum Coexistence,” John Wiley & Sons, 17 November 2006

• Matthew S. Gast, “802.11 Wireless Networks: The Definitive Guide,” O'Reilly Media, 6 May 2005

• Andreas Molisch, “Wireless Communications,” John Wiley & Sons, 23 September 2005



Many thanks for your attention!

Tutorial on radio communications:

From the basics to future developments

Part 3: Advances in wireless LANs

Oliver Hoffmann

Dortmund University of Technology

[email protected]

advances in wlans - chungbuk.ac.krcommlab.chungbuk.ac.kr/lab/lecture2/lecture2_1/12....

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